The present invention relates to a failure diagnosis apparatus for a homogeneous charge compression ignition engine that compresses and ignites a mixture of fuel and air in a combustion chamber.
Japanese Laid-Open Patent Publication Nos. 3-9010 and 6-317117 each describe a variable valve timing mechanism, which varies the valve timing of an intake valve or an exhaust valve according to the driving state of an internal combustion engine. When a failure occurs in a variable valve timing mechanism of an internal combustion engine, the actual valve timing may differ from the target valve timing and thereby lower the driving performance of the engine.
The above publications each describe an apparatus for diagnosing a variable valve timing mechanism to determine whether a failure has occurred in the mechanism. The apparatus described in Japanese Laid-Open Patent Publication No. 3-9010 determines whether a failure has occurred in the variable valve timing mechanism based on a valve timing varying signal and a detected intake amount.
The apparatus described in Japanese Laid-Open Patent Publication No. 6-317117 determines whether a failure has occurred in the variable valve timing mechanism based on the pulsation level of intake air detected by an intake air pulsation detector and a predetermined pulsation level corresponding to each driving condition of the internal combustion engine.
A homogeneous charge compression ignition (HCCI) engine generates a small amount of NOx and practically no soot. However, an HCCI engine may experience misfiring and knocking more frequently than a spark-ignition internal combustion engine. Japanese Laid-Open Patent Publication No. 2005-315126 describes an HCCI engine that assists homogeneous charge compression ignition using the heat of the exhaust gas by performing spark ignition or internal exhaust gas recirculation (EGR) when necessary. The internal EGR keeps exhaust gas in a combustion chamber or re-circulates exhaust gas into the combustion chamber. The engine described in Japanese Laid-Open Patent Publication No. 2005-315126 performs both homogeneous charge compression ignition and spark ignition, which have different optimum valve timing settings. Therefore, the engine described in Japanese Laid-Open Patent Publication No. 2005-315126 needs a variable valve timing mechanism.
However, Japanese Laid-Open Patent Publication Nos. 3-9010 and 6-317117 do not describe a failure diagnosis for an HCCI engine that performs both homogeneous charge compression ignition and spark ignition.